Method for operating a heating element

ABSTRACT

The invention relates to a method for operating a heating element (210), in particular in a food processor (1) for the at least partially automatic preparation of foodstuffs, wherein the following steps are performed: a) detecting an electrical resistance of the heating element (210) such that at least one resistance value is determined, b) performing a heating operation on the heating element (210) based on the at least one determined resistance value to perform the heating operation depending on a temperature of the heating element (210).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European application no. 18 152116.2 filed on Jan. 17, 2018, which is hereby incorporated by referencein its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method of operating a heatingelement, in particular a kitchen appliance. Furthermore, the inventionrefers to a detection device, a heating system, a food processor withthe heating system and a computer program product for operating theheating element.

2. Background

It is known in food processors that heating systems are used to heat amedium. A temperature is often set to which the medium is to be heated,e.g. automated or set by a user of the food processor. In order to nowoperate a heating element of the heating system in such a way that thistemperature is reached and maintained, a heating, and in particular atemperature control can conventionally be carried out, which uses ameasurement of a separate temperature sensor, such as an NTC resistor,for the control (as controlled parameter).

A disadvantage of the known solutions for the operation of a heatingelement, especially for heating control, is that the temperature cannotbe reliably maintained. For example, it can happen that an inhomogeneousmedium (e.g. different foodstuffs as medium) causes a local temperaturechange in the heating element. These so-called hotspots on the heatingelement can cause the medium to burn at these points.

SUMMARY

It is therefore an object of the present invention to at least partiallyeliminate the disadvantages described above. In particular, it is theobject of the present invention to provide an improved heating controlwithout complex measuring sensors or measuring sensor technology.

The preceding object is solved by a method with the features of theindependent method claim, by a detection device with the features of theindependent device claim, by a heating system with the features of theindependent system claim, by a food processor with the features of thefurther independent device claim, and by a computer program product withthe features of the corresponding further independent device claim.Further features and details of the invention result from the respectivedependent claims, the description and the drawings. Features and detailswhich are described in connection with the method according to theinvention also apply, of course, in connection with the device accordingto the invention, the heating system according to the invention, thefood processor according to the invention as well as the computerprogram product according to the invention, and vice versa in each case,so that with regard to the disclosure of the individual aspects of theinvention mutual reference is or can always be made.

The object is solved in particular by a method for operating a heatingelement, such as a heater, in particular in a food processor or kitchenappliance (such as a kettle, oven or stove, etc.) for at least partiallyautomatic preparation of foodstuffs.

It is advantageous that at least one of the following steps can becarried out in a method according to the invention, whereby the stepsare preferably carried out one after the other or in any order, and ifnecessary individual steps can also be repeated:

-   -   a) Detection of an electrical resistance of the heating element        so that at least one resistance value is determined,    -   b) Carrying out a heating operation in the heating element using        the at least one determined resistance value, wherein for this        purpose the at least one determined resistance value is        preferably evaluated by an evaluation device, and in particular        a temperature of the heating element is determined using the at        least one determined resistance value in order to carry out the        heating operation as a function of the temperature.

In other words, the (currently) determined resistance value, which isspecific for the electrical resistance of the heating element (calledresistance for short), can (preferably directly) serve as a basis forthe temperature-dependent heating operation. This heating operation istherefore to be understood in particular as a control (hereinafter also:heating control, temperature control) in which the temperature of theheating element and thus the (currently available) resistance, which isspecific to the (respective) temperature, serves as the controlledparameter. For example, the resistance value can be evaluated (and ifnecessary also processed), preferably compared with a setpoint value forthe temperature or the resistance, in order to determine a controldifference through the comparison. Thus, an additional temperaturesensor can be dispensed with in the method according to the invention.Preferably, an (electronic) controller can be used for control to enablethis heating operation. For heating operation, an energy source, such asan AC voltage source, can be used to transfer energy to the heatingelement to create an electrical current flow through the heating element(to generate heat and heat the medium). For example, the heatingoperation is clocked and/or according to a switching frequency, withwhich energy is transferred from the energy source to the heatingelement. By varying the switching frequency (e.g. by controllingsemiconductor switches) the energy transfer and thus the temperature ofthe heating element can be influenced, and thus also the heating control(or temperature control) can be enabled. Advantageously, a temperature,in particular a medium temperature (of a medium in the area of theheating element, e.g. in the stirring vessel), can thus be determined onthe basis of electrical parameters of the heating element, in particularof a thick-film heater.

Preferably, according to step a), the resistance of the heating elementis detected as an electrical resistance of an electrical conductor ofthe heating element through which an electrical current is conducted togenerate heat (in particular due to the heating of the conductor). Atthe same time, by recording the resistance, a resistance value can bedetermined which indicates the temperature caused by this heatgeneration. In particular, the heating function is provided by theheating of the conductor.

The advantage of using the resistance value to provide temperaturedependency during heating operation is that a particularly reliable andtechnically simple way of carrying out heating operation is possible, atwhich the temperature can be set very precisely. Additional sensors fortemperature measurement can also be dispensed with in order to furtherreduce costs and complexity.

Preferably in step b) a temperature value is determined on the basis ofat least one determined resistance value, and this temperature value isused as an input value for heating operation, in particular heatingcontrol. Alternatively, at least one determined resistance value can beused directly (without conversion) as an input value, e.g. as acontrolled parameter. The latter case is also understood as adetermination of the temperature (e.g. according to step b)), since thisdoes not necessarily require the conversion into an absolute temperaturevalue. Rather, the determination of the at least one resistance valuecan already include the determination of the temperature, since theresistance of the heating element is specific to the temperature of theheating element.

In particular, the heating element is part of a heating system,preferably for heating a medium, e.g. in a stirring vessel of a foodprocessor. Surprisingly, it was found that the ohmic resistance of theheating element, especially of a thick-film heater, is proportional tothe temperature of the heater. This enables to technically measure theelectric current and/or the electric voltage with activated heating andto calculate the resistance. Thus, the electrical (i.e. ohmic)resistance of the heater can serve as the basis for temperature control.

It is advantageous if, depending on at least one resistance value, amedium temperature of a medium in a stirring vessel of the foodprocessor is determined. For example, empirically determinedrelationships can be used for this purpose, which can preferably bestored electronically in a data base and/or in a data memory by means ofa function sequence, in order to be able to calculate or determine themedia temperature from at least one resistance value. For example, withthe known structure and configuration of the stirring vessel, it ispossible that the influence of the heating element on the medium in thestirring vessel can be predetermined. It may be advantageous to providethat the type of medium is also known, e.g. by entering a user at thefood processor. It may also be possible for the heating control to becarried out on the basis of the resistance value, in particular forheating at least one foodstuff in a stirring vessel of the foodprocessor, the heating element being fixed to the stirring vessel, inparticular being integrated in a base of the stirring vessel.

A further advantage can be achieved by the fact that the detection ofthe electrical resistance (according to step a)) is understood as atwo-dimensional temperature monitoring of the heating element. Theheating element preferably has a flat formation and/or extension so thatlocal temperature changes, such as hotspots, may occur in the heatingelement. Hotspots are local temperature increases, which can locallychange the resistance of the heating element. These are caused, forexample, by different heat capacities at the heating element, i.e. amedium is only partially in heat exchange with the heating element (e.g.due to an inclination of the stirring vessel or due to an inhomogeneouscomposition of the medium in the stirring vessel). Based on anevaluation of at least one determined resistance value, a detection ofthese hotspots can be made possible, i.e. an area-wide monitoring cantake place.

It is also conceivable that in step a) a temporal course of resistancevalues is determined, whereby a local temperature change, in particularhotspots, in the heating element is determined on the basis of anevaluation of the course.

The invention may also provide for the “medium” to refer to the contentsof the stirring vessel, i.e. to include different substances and/orfoodstuffs.

The use of the electrical resistance of the heating element as the basisfor heating operation, in particular temperature control, has thefurther advantage that the temperature can also be recorded at highswitching frequencies of the heating element (e.g. above 2 kHz).Advantageously, the heating element can be operated with a switchingfrequency in the range from 2 kHz to 40 kHz, preferably 10 kHz to 30kHz, preferably 20 kHz.

For example, it may be possible that during heating operation theheating element is controlled with a switching frequency that isparticularly greater than 1 kHz or greater than 2 kHz. The heatingelement is preferably configured as a thick-film heater.

It may also be possible that the heating operation is carried out astemperature control of the heating element with the temperature of theheating element as controlled parameter. Thus the temperature controlcan be carried out efficiently, especially as a heating control for theheating element for heating a medium, and e.g. a burning of the mediumcan be avoided.

It is also conceivable that during heating operation the temperature forheating operation can only be determined on the basis of the resistancedetected or on the basis of at least one resistance value, so that aseparate temperature sensor (e.g. NTC sensor, i.e. a heat conductor) canbe dispensed with. This has the advantage that costs and installationspace are saved and, for example, the number of plug contacts in astirring vessel can be reduced.

In addition, it may be provided that during the heating operation of theheating element for heating control, the resistance is repeatedlydetected in accordance with step a), the resistance value (in accordancewith step a)) in each case being determined by comparing at least onemeasured current value from a current measurement in the heating elementand at least one measured voltage value from a voltage measurement inthe heating element with one another. This has the advantage that duringheating operation, i.e. with active heating, the temperature of theheating can be determined reliably and efficiently. Advantageously, thecomparison for determining the resistance value can be made by dividingthe measured voltage and current values.

A further advantage within the scope of the invention can be achieved ifa local temperature change in the heating element is detected and/orrecorded on the basis of the at least one resistance value, whereinpreferably in step b) a (temporal) change characteristic of thedetermined resistance values is evaluated for this purpose, whereinpreferably in step a) a temporal characteristic and/or a gradient of theresistance values is determined for this purpose. For example, in stepa) several resistance values can be determined for different points intime, e.g. cyclically and/or at regular intervals. The acquisition times(measurement times) at which the resistance values have been determinedare also determined and/or temporarily stored in preference. In otherwords, a resistance gradient can be calculated on the basis of thedetermined resistance values and the associated measurement times. Astrong change of the gradient (e.g. a sudden increase) can indicate ahotspot, which locally changes the resistance of the heating element.Thus, the change characteristic (i.e. a change in the gradient) canindicate a local change in resistance, in particular a hotspot. This canbe used, for example, to lower the temperature of the heating and thusavoid burning the medium (e.g. foodstuffs).

It is also advantageous if a resistance gradient is determined by arepeated acquisition of the resistance during heating operation, wherebya time of acquisition is determined for the respective resistance valuesand, in particular, stored with the respective resistance value. Inparticular, the acquisition times can be assigned to the correspondingresistance values, e.g. by a table and/or in a database and/or by usingan electronic (e.g. digital) pointer which makes the assignment. Forexample, the stored acquisition times and/or the stored resistancevalues are read out and processed by an evaluation device in order tocalculate a resistance gradient.

Optionally, it may be possible that in step a) the total resistance ofthe heating element is measured, i.e. the electrical resistance isdetermined over the entire surface of the heating element. In otherwords, a resistance value can be determined according to step a), whichis specific to the total resistance of the heater. It is advantageous ifthe heating operation is carried out as temperature control and thetemperature of the heating element is determined exclusively on thebasis of the resistance measurement (according to step a)) of theheating element, i.e. in particular without using a separate temperaturesensor, such as an NTC resistor. In this way, costs and technicalexpenditure can be significantly reduced if the heating operation iscarried out as temperature control with the temperature as thecontrolled parameter.

Advantageously, it may be provided in the invention that at or afterstep b) an analysis of the at least one determined resistance value, andin particular further information about the heating element and/or abouta medium in a stirring vessel of the food processor, is carried out,wherein at least one of the subsequent analysis results is determined bythe analysis:

-   -   at least one information on a local temperature change in the        heating element,    -   (at least one information about) a temperature of the medium,    -   at least one information on at least one heat capacity of the        medium,    -   at least one information on a composition of the medium, in        particular a type and/or an amount of at least one foodstuff in        the stirring vessel.

For example, the analysis can be carried out by an evaluation device.For this purpose, the evaluation device may be connected, for example,to an electronic data memory in order to read information from the datamemory for analysis. For analysis, a comparison of this information withat least one resistance value can be carried out if necessary. Forexample, the information is determined empirically and/or statistically.This means that it is used that certain resistance characteristics orresistance gradient characteristics can indicate further information,which may have to be empirically determined beforehand. For example, theanalysis of the resistance values can be used to determine if anincrease in resistance of 3 ohms in a certain period of time, e.g.within a maximum of 1 s or within a maximum of 2 s or within a maximumof 5 s or within a maximum of 10 s or within a maximum of 20 s, occursin order to detect a local temperature change, in particular a hotspot.The analysis can also correlate at least one determined resistance valuewith a medium temperature. The evaluation device is configured e.g. aselectronics and/or as microcontroller and/or as processor and/or as atleast one integrated circuit.

Another object of the invention is a detection device for operating aheating element, preferably for detecting resistance in the heatingelement, in particular in a food processor for the at least partiallyautomatic preparation of foodstuffs:

-   -   a voltage measuring device for measuring an electrical voltage        at the heating element,    -   a current measuring device for measuring an electric current at        the heating element,    -   an evaluation device for detecting, in particular determining        and/or calculating, an electrical resistance in the heating        element by evaluating at least one (voltage) detection value of        the voltage measuring device and at least one (current)        detection value of the current measuring device, so that        preferably at least one resistance value can be determined in        order to provide the at least one resistance value for a        temperature-dependent heating operation, in particular heating        control, of the heating element.

Thus, the inventive recording device has the same advantages as havebeen described in detail with regard to a method according to theinvention. In addition, the detection device may be configured to beoperated in accordance with a method in accordance with the invention.

In addition, it may be advantageous in the context of the invention thatthe voltage measuring device comprises an active rectifier, so that avoltage drop in diodes of the voltage measuring device can be at leastpartially or predominantly compensated. The active rectifier canpreferably compensate for the voltage drop across the diodes so thatvoltages below the blocking voltage of the diodes (e.g. below 0.7 V) canalso be rectified and measured. This allows very efficient voltagemeasurement by the active rectifier.

Another object of the invention is a heating system for operating aheating element, in particular in a food processor for the at leastpartially automatic preparation of foodstuffs:

-   -   a detection device, preferably a detection device according to        the invention, it being advantageous for the detection device to        detect an electrical resistance in the heating element,    -   a control device, in particular a control device such as a        regulator, for controlling, preferably regulating, the operation        of the heating element, the control device being electrically        connected to the detection device in order to carry out the        control on the basis of the detection of the resistance.

Thus, the heating system according to the invention has the sameadvantages as those described in detail with regard to a methodaccording to the invention and/or a detection device according to theinvention. In addition, the heating system may be suitable to beoperated according to a method in accordance with the invention.

Also protected is a food processor for at least partially automaticpreparation of foodstuffs, comprising:

-   -   a stirring vessel for receiving and preparing the foodstuffs,    -   a heating system according to the invention, whereby the heating        system is equipped with a heating element which is integrated in        the stirring vessel.

As an option, it may be possible for the heating element to beintegrated in a stirring vessel of the food processor, so that atemperature which can be determined according to the heating systemaccording to the invention on the basis of the resistance detected isspecific for a temperature of a medium in the stirring vessel. Forexample, the correlation between the temperature of the heating elementand the medium can be used to reliably determine the temperature of themedium on the basis of empirical information, which is pre-stored in adata memory, for example.

Optionally, it may be provided that the heating element is integratedinto an agitator vessel bottom of an agitator vessel of the foodprocessor and extends therein flatly for heating a medium in theagitator vessel (so that preferably the detected resistance is specificfor a temperature of the medium in the agitator vessel). In particular,the heating element may extend over at least 50% or at least 70% or atleast 80% or at least 90% of the total area of the bottom of theagitator vessel. This allows the medium in the stirring vessel to beheated reliably. Alternatively or additionally, it is possible that theheating element is configured as a thick-film heater in order toefficiently heat the medium.

In accordance with an advantageous further development of the invention,it can be provided that an electrical current flowing through theheating element is detected in order to detect the resistance, whereby ashunt resistor is preferably connected in series with the heatingelement in order to detect the electrical current through the heatingelement. It may also be possible that an electrical voltage across theshunt resistor is measured and/or amplified by an operational amplifierin order to measure the current, and if necessary the operationalamplifier is connected with an offset voltage to increase themeasurement potential. Thus, the voltage and/or a voltage differenceacross the shunt can be amplified by the operational amplifier so that,for example, an analog-to-digital converter (ADC) of the evaluationdevice (e.g. as a microcontroller) can measure it sufficientlyaccurately. So that no negative voltage values are present at the ADC,the operational amplifier can be connected with the offset voltage inorder to increase the measuring potential for current measurement at theheating element accordingly. It is also advantageous if the recording ofthe current, in particular current measurement, is only carried out whenthe heating is active.

Another object of the invention is a computer program product foroperating a heating element. In accordance with an advantage of theinvention, the computer program product is configured to initiate theexecution of the following steps when executed by an evaluation device:

-   -   a) Detection of an electrical resistance of the heating element        so that at least one resistance value is determined,    -   b) Carrying out a heating operation in the heating element using        the at least one determined resistance value, preferably the at        least one determined resistance value being evaluated,        preferably a temperature of the heating element being determined        using the at least one determined resistance value in order to        carry out the heating operation as a function of the        temperature.

Thus, the computer program product according to the invention has thesame advantages as those described in detail with regard to the methodaccording to the invention. In addition, the computer program productcan be configured to initiate or map the steps of an inventive method.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention result fromthe following description, in which embodiments of the invention aredescribed in detail with reference to the drawings. The featuresmentioned in the claims and in the description may be essential to theinvention either individually or in any combination. It is shown:

FIG. 1 a schematic representation of a current measuring device,

FIG. 2 a schematic representation of the use of an offset voltage forcurrent measurement,

FIG. 3 a schematic representation of a voltage measuring device withactive rectifier,

FIG. 4 a schematic representation of a food processor according to theinvention, and

FIG. 5 a schematic representation of a change characteristic.

In the following figures, the identical reference signs are used for thesame technical characteristics, even for different execution examples.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

FIGS. 1, 3 and 4 schematically illustrate parts of a heating system 200for a food processor 1 according to the invention. Furthermore, FIGS. 1to 5 serve to represent a detection device 240 in accordance with theinvention and to visualize a process in accordance with the invention.

FIG. 1 shows that an inventive detection device 240 may have a currentmeasuring device 242. The current measuring device 242 is used tomeasure an electrical current flowing through a heating element 210, inparticular a thick-film heater 210, in a load circuit 250 of a heatingsystem 200. According to ohmic law, this current is linked to anelectrical resistance of the heating element 210 and in particular isalso dependent on and, if necessary, proportional to a temperature ofthe heating element 210, at least for a partial temperature range. Thus,the current measurement (if necessary together with a voltagemeasurement) can be used for heating control, e.g. for the control of apower supply of the heating element 210 by a voltage source 260.Accordingly, a supply voltage marked U1 in FIG. 1 (in particular as analternating voltage) can be used and/or changed according to the heatingregulation by a control device 220 in order to carry out a heating of amedium 20 e.g. in a stirring vessel 2 of a food processor 1.Furthermore, an input voltage U2 via shunt resistor 242.1 is shown,which can be amplified by an operational amplifier OP (with adifferential voltage U5). This may still be connected to an offsetvoltage U3 of a corresponding voltage source 242.2 in order to obtain anoutput voltage U4. Further resistors R may be provided for the circuit,which may also have different resistance values.

For current measurement the shunt resistor 242.1 is used, which can beintegrated serially to the heating element 210 in the load circuit 250.A voltage difference U5, which is dependent on the input voltage U2 overthe shunt resistor 242.1, is amplified by means of at least oneoperational amplifier OP, so that an evaluation device 243, inparticular an analog-to-digital converter (ADC) of this evaluationdevice 243, e.g. of a microprocessor, can measure this sufficientlyaccurately. So that no negative voltage values are present at theevaluation device 243 or at the ADC, the operational amplifier OP can beconnected with the offset voltage U3, which raises the measuringpotential. This is also shown in FIG. 2 (the increase is represented byan arrow). In this way, a current value of a current at heating element210 can be determined very reliably on the basis of the voltage value ofthe output voltage U4.

FIG. 3 shows that the detection device 240 may also include a voltagemeasuring device 241 to detect an electrical voltage at the heatingelement 210. This can include a voltage divider (shown here with aninput L, two resistors R and a ground potential GND) to provide an inputvoltage not explicitly marked as a measurement voltage. The circuitshown in FIG. 3 also includes an active rectifier to compensate for avoltage drop across the diodes D shown in FIG. 3 so that voltages belowthe reverse voltage of the diodes D (e.g. below 0.7 V) can also berectified and measured. This enables to provide a very reliable andhighly accurate voltage value for controlling the heating element. Thevoltage value determined by the circuit shown in FIG. 3 can be usedtogether with the current value measured by the current measuring device242 to determine a resistance value of a resistance of the heatingelement 219.

FIG. 4 schematically shows a food processor 1 comprising a stirringvessel 2 into which a medium 20 (with at least one foodstuff) can befilled. The stirring vessel 2 can be detachably connected to a holder ofthe food processor 1 and have a stirrer 3. A heating element 210 of aheating system 200 can also be integrated in a bottom 2.1 stirringvessel to heat the medium 20. An evaluation device 243 and a detectiondevice 240 may also be provided for heating control.

FIG. 5 schematically shows a change characteristic C (with resistancevalues of a resistance R of the heating element 210 over time t). Thedashed line shows the determined resistance values of a detectedresistance of the heating element 210, which can be used to determine atemperature of the heating element 210 or the medium 20. This iscontrasted with a further curve showing the course of a measuredtemperature value by a separate sensor. Both curves clearly show aheating-up phase 280, whereas the further course after the heating-upphase 280 differs. Only in the dotted curve (i.e. also according to thetemperature determined by the resistance of the heating element 210according to the invention) is the formation of a so-called hotspotsrecognizable. In the present case, the stirring vessel 2 was tilted, sothat the medium was only partially in heat-transmitted contact with theheating element 210. A similar effect may be caused, for example, by aninhomogeneous medium due to the foodstuffs prepared.

The preceding description of the embodiments describes the presentinvention exclusively in the context of examples. Of course, individualfeatures of the embodiments can be freely combined with each other, iftechnically reasonable, without leaving the scope of the presentinvention.

REFERENCE LIST

1 food processor

2 Stirring vessel

2.1 Stirring vessel bottom

3 Agitator

20 Medium

200 Heating system

210 Heating element, thick-film heating

220 Control device

240 Detection device

241 Voltage measuring device

242 Current measuring device

242.1 Shunt resistance

242.2 Offset voltage

243 Evaluation device

250 Load circuit

260 Voltage source, AC voltage source

280 Heating phase

281 Inclination of the pot, Hot-Spot

t time

C Change characteristics

D Diode

GND Ground potential

OPO operational amplifier

R Resistance

U1 supply voltage

U2 Input voltage

U3 Offset voltage

U4 Output voltage

U5 Differential voltage

What is claimed is:
 1. A method for operating a heating element, inparticular in a food processor for at least partially automaticpreparation of foodstuffs, wherein the following steps are performed: a)detecting an electrical resistance of the heating element such that atleast one resistance value is determined, b) performing a heatingoperation on the heating element based on the at least one determinedresistance value to perform the heating operation depending on atemperature of the heating element.
 2. The method according to claim 1,wherein the heating operation is carried out as temperature control ofthe heating element with the temperature as controlled parameter.
 3. Themethod according to claim 1, wherein the resistance is repeatedlydetected in accordance with step a) during heating operation, theresistance value in each case being determined by comparing at least onemeasured current value from a current measurement in the heating elementand at least one measured voltage value from a voltage measurement inthe heating element with one another.
 4. The method according to claim1, wherein a local temperature change in the heating element is detectedbased on the at least one resistance value, preferably in that in stepb) a change characteristic of the determined resistance values isevaluated, wherein preferably for this purpose in step a) at least atemporal course or a gradient of the resistance values is determined. 5.The method according to claim 1, wherein a resistance gradient isdetermined by repeated detection of the resistance during the heatingoperation, a detection time being determined for this purpose forrespective resistance values.
 6. The method according to claim 5,wherein the detection time being stored with the respective resistancevalue.
 7. The method according to claim 1, wherein the total resistanceof the heating element is detected in step a), preferably the heatingoperation being carried out as a temperature control in accordance withstep b) by determining the temperature in the heating element fortemperature control exclusively on the basis of the detection of thetotal resistance of the heating element in accordance with step a). 8.The method according to claim 1, wherein at or after step b) an analysisof the at least one determined resistance value is carried out, at leastone of the subsequent analysis results being determined by the analysis:information about a local temperature change in the heating element, atemperature of the medium, information about at least one heat capacityof the medium, information on a composition of the medium.
 9. The methodaccording to claim 8, wherein analysis results being determined by theanalysis of information on a composition of the medium, at least a typeor an amount of at least one foodstuff in the stirring vessel.
 10. Adetection device for operating a heating element, in particular in afood processor for at least partially automatic preparation offoodstuffs, comprising: a voltage measuring device for measuring anelectric voltage at the heating element, a current measuring device formeasuring an electric current at the heating element, an evaluationdevice for detecting an electrical resistance in the heating element byevaluating detection values of the voltage measuring device and thecurrent measuring device, such that at least one resistance value can bedetermined in order to provide the at least one resistance value for atemperature-dependent heating operation of the heating element.
 11. Thedetection device according to claim 10, wherein the voltage measuringdevice comprises an active rectifier so that a voltage drop in diodes ofthe voltage measuring device can be compensated at least partially orpredominantly.
 12. The detection device according to claim 10, whereinthe detection device is adapted to perform a method for operating aheating element for the at least partially automatic preparation offoodstuffs, wherein the following steps are performed: a) detecting anelectrical resistance of the heating element such that at least oneresistance value is determined, b) performing a heating operation on theheating element based on the at least one determined resistance value toperform the heating operation depending on a temperature of the heatingelement.
 13. A heating system for operating a heating element for atleast partially automatic preparation of foodstuffs, comprising:detection device for detecting an electrical resistance in said heatingelement, a control device for controlling the heating element, thecontrol device being electrically connected to the detection device toperform the control based on the detection of the resistance.
 14. Theheating system according to claim 13, wherein the heating system isconfigured to at least perform a method for operating a heating elementfor the at least partially automatic preparation of foodstuffs, whereinthe following steps are performed: a) detecting an electrical resistanceof the heating element such that at least one resistance value isdetermined, b) performing a heating operation on the heating elementbased on the at least one determined resistance value to perform theheating operation depending on a temperature of the heating element, orthe detection device is configured for operating a heating element forthe at least partially automatic preparation of foodstuffs, comprising:a voltage measuring device for measuring an electric voltage at theheating element, a current measuring device for measuring an electriccurrent at the heating element, an evaluation device for detecting anelectrical resistance in the heating element by evaluating detectionvalues of the voltage measuring device and the current measuring device,such that at least one resistance value can be determined in order toprovide the at least one resistance value for a temperature-dependentheating operation of the heating element.
 15. A food processor for atleast partially automatic preparation of foodstuffs, with: a stirringvessel for receiving and preparing the foodstuffs, a heating system foroperating a heating element for at least partially automatic preparationof foodstuffs, comprising: detection device for detecting an electricalresistance in said heating element, a control device for controlling theheating element, the control device being electrically connected to thedetection device to perform the control based on the detection of theresistance in which a heating element is integrated into the stirringvessel.
 16. The food processor according to claim 15, wherein at leastthe heating element is integrated into a base of the stirring vessel ofthe food processor, and extends flatly therein for heating a medium inthe stirring vessel, so that an electrical resistance of the heatingelement is specific for a temperature of the medium in the stirringvessel, or in that the heating element is configured as a thick-filmheater.
 17. A computer program product for operating a heating element,the computer program product being adapted to initiate execution of thefollowing steps when executed by an electronic evaluation device: a)detecting an electrical resistance of the heating element such that atleast one resistance value is determined, b) carrying out a heatingoperation on the heating element using the at least one determinedresistance value in order to carry out the heating operation as afunction of a temperature of the heating element.
 18. The computerprogram product according to claim 17, wherein a method for operating aheating element for at least partially automatic preparation offoodstuffs, is carried out by executing the computer program product toperform the following steps: a) detecting an electrical resistance ofthe heating element such that at least one resistance value isdetermined, b) performing a heating operation on the heating elementbased on the at least one determined resistance value to perform theheating operation depending on a temperature of the heating element.